1. Field of the Invention
The present invention relates to a vibratory gyro piezoelectric vibrator and, in particular, to a structure of a piezoelectric vibrator including a vibrating body, which has a length extending in a lamination direction of a plurality of laminated piezoelectric layers and takes advantage of a longitudinal piezoelectric effect of the piezoelectric layers.
2. Description of the Related Art
Conventionally, a piezoelectric tuning bar and a piezoelectric tuning fork are known as a piezoelectric vibrator for a vibratory gyro. For example, Japanese Unexamined Patent Application Publication No. 8-320233 discloses a piezoelectric tuning bar having piezoelectric elements disposed on three sides of a right-triangular-pillar-shaped vibrating body made of metal. The piezoelectric tuning bar bends and vibrates the vibrator in a direction that is perpendicular to the surface having the piezoelectric elements in response to the application of an alternating voltage to the piezoelectric elements.
Furthermore, for example, Japanese Unexamined Patent Application Publication No. 9-269227 discloses a piezoelectric tuning bar having a pillar-shaped vibrating body, which has a length extending in a direction that extends in the direction that is perpendicular to the thickness direction of two pasted piezoelectric substrates. The piezoelectric substrates are polarized in the opposite direction of the thickness direction. Here, main surfaces of the vibrating body are opposed in the thickness direction of the vibrating body and have external electrodes provided thereon. In response to application of alternating voltage to these external electrodes, the vibrating body is bent and vibrated in the thickness direction of the piezoelectric substrate. Since a piezoelectric tuning fork has a similar construction as that of a piezoelectric tuning bar and the construction is publicly known, the descriptions will be omitted herein.
Both of these piezoelectric vibrators take advantage of a characteristic that, in response to application of alternating voltage to electrodes on both sides of the piezoelectric body in the polarization direction, a piezoelectric body stretches in the direction perpendicular to a direction of the voltage application. In other words, a plate-shaped piezoelectric body stretches in the plane direction in response to application of voltage to electrodes on both of the front and back surfaces of the piezoelectric body, which is polarized in the thickness direction. This characteristic is called a lateral piezoelectric effect (d31 effect).
In reality, a piezoelectric body stretches also in the thickness direction in response to application of voltage, and the characteristic is called a longitudinal piezoelectric effect (d33 effect). However, conventionally, a general piezoelectric vibrator does not actively use a longitudinal piezoelectric effect. This is because the stretch due to a longitudinal piezoelectric effect is smaller than the stretch due to a lateral piezoelectric effect.
In recent years, more and more electronic components are lead-free, and materials containing a lead component tend to be not used as a result. Furthermore, since many conventional piezoelectric materials contain a lead component, new piezoelectric vibrators which contain piezoelectric materials without a lead component are being demanded. However, a piezoelectric material without a lead component produces a small amount of stretch from a lateral piezoelectric effect, which is a problem. Therefore, using a piezoelectric material without a lead component is difficult for a piezoelectric vibrator having a conventional structure.
In order to produce a piezoelectric vibrator containing a piezoelectric material without a lead component, a longitudinal piezoelectric effect may be actively used instead of a lateral piezoelectric effect. In other words, a vibrating body may include a laminate of multiple piezoelectric layers stacked in a lamination direction and has a length extending in the direction of the laminate. A sum of longitudinal piezoelectric effects of the piezoelectric layers of the vibrating body may result in a certain amount of stretch of the entire integrated vibrating body.
As an example of a piezoelectric vibrator having the laminate structure, Japanese Unexamined Patent Application Publication No. 2003-69372 discloses a structure that is not for a vibratory gyro. The piezoelectric vibrator includes an integral vibrating body having a laminate of multiple piezoelectric layers polarized in the thickness direction, which is coincident with the lamination direction. In the laminate, the piezoelectric layers alternately have opposite polarization directions from each other. A piezoelectric layer between a first internal electrode and a third internal electrode and a piezoelectric layer between a second internal electrode and the third internal electrode are alternately opposed to each other. These internal electrodes are provided in substantially an entire area in the thickness direction or width direction of the vibrating body, which is perpendicular to the lamination direction in both cases.
Furthermore, the longitudinal direction is coincident with the lamination direction on a main surface on one side of the vibrator in the thickness direction. First and second external electrodes are arranged in parallel through a channel portion in the width direction perpendicular to both of the lamination direction and the thickness direction. The first and second internal electrodes are spaced from each other in parallel and are connected to and are conducted to the first and second external electrodes, respectively. The third internal electrode is not connected to any of the external electrodes and is electrically floating.
When an alternating voltage from the first and second external electrode is input to a piezoelectric vibrator disclosed in Japanese Unexamined Patent Application Publication No. 2003-69372, that is, a piezoelectric vibrator having the laminate structure, piezoelectric layers of the vibrator have opposite polarization directions from each other and stretch because of the longitudinal piezoelectric effect. Here, a piezoelectric layer between a first internal electrode and a third internal electrode and a piezoelectric layer between a second internal electrode and the third internal electrode stretch in the opposite directions from each other. As a result, the vibrating body bends and vibrates in the width direction of the vibrating body, which is perpendicular to the lamination direction of the piezoelectric layer as a whole.
The conventional piezoelectric vibrator requires a resonator mainly using an electric characteristic. Furthermore, the piezoelectric vibrator has a laminate structure because using bending vibration based on stretching due to a longitudinal piezoelectric effect is more advantageous in reduction of the size of the entire structure than using direct stretching due to a lateral piezoelectric effect. However, while a first bending vibration is being excited in which a vibrating body bends in the direction that is perpendicular to the lamination direction of piezoelectric layers in the piezoelectric vibrator and when an angular velocity about the lamination direction as the axis of rotation is applied to the piezoelectric vibrator, second bending vibration may be excited by the action of a Coriolis force. Here, in the second bending vibration, the vibrating body bends in the direction that is perpendicular to both of the lamination direction and the vibration direction of the first bending vibration.
However, since the piezoelectric vibrator does not have a detecting unit for detecting an output from the second bending vibration, the piezoelectric vibrator cannot detect an output caused by the second bending vibration. Thus, the piezoelectric vibrator cannot be used as a vibratory gyro.